My ears are plugged up and hearing is muffled. What should I do?

Fluid behind eardrum. Go see your doctor to check for fluid behind your eardrum or impacted ear wax or other obstruction of the ear canal. Fluid build up is not unexpected with allergies and viruses.
Ear Wax? It is possible you have what we call a "cerumen impaction" with the plugged up feeling you described, which just a fancy way of saying ear wax is blocking your ear canals. The only way to know for sure is to visit your doctor as there are many other causes. If it is ear wax, avoid q-tips as it acts as a plunger and consider trying debrox that is over the counter.